Initiators for carbocationic polymerization of olefins

ABSTRACT

A new class of initiators for inducing the cationic polymerization of olefins was discovered. These initiators, in conjunction with Lewis acids as coinitiators, effectively initiate the carbocationic polymerization of olefins. The new initiators are epoxides with the general formula  
                 
 
     where R 1 , R 2  and R 3  are hydrogen, alkyl, aryl or aralkyl groups, and can be the same or different, and i is a positive whole number. The Lewis acid has the general formula of MtX n  where M is titanium, aluminum, boron or tin, X is a halogen, an alkyl or an alcoxy or a mixture thereof. The process is a carbocationic process, which can be living or non-living, at a temperature of from about  0  to  −80  C. The polymer produced can be a homo- or copolymer (random or block) carrying hydroxy functional groups.

REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of application Ser. No. 09/176,748, filedOct. 22, 1998.

BACKGROUND OF THE INVENTION

[0002] The carbocationic polymerization of olefins is well-known and hasbeen studied in detail. These processes can be initiated by systemsproducing carbocations. These initiating systems include Lewis andBronsted acids, organic compounds such as halides in conjunction withLewis acids, etc. (J. P. Kennedy: Cationic Polymerization of Olefins: ACritical Inventory. Wiley-Intersci). These processes produce high or lowmolecular weight polymers with various halide or olefinic functionalgroups, and can be further functionalized by post-polymerizationreactions.

[0003] The living carbocationic polymerization of olefins such asisobutylene and styrene is a relatively new development. Prior artdescribes living carbocationic polymerizations producing polymers withcontrolled molecular weights and molecular weight distributions as lowas M_(w)/M_(n)=1.05 (see U.S. Pat. No. 5,169,914). Suitable initiatorsinclude compounds with tertiary functional groups of the general formulashown below:

[0004] where R₁, R₂ and R₃ can be hydrogen or aliphatic or aromaticalkyl groups, or aralkyl groups, and X can be a halogen, hydroxyl, etheror ester groups, or peroxides. These initiators, in conjunction withLewis acids, Electron Pair Donors and Proton Traps, have successfullybeen used to produce homopolymers and random or block copolymers. Theprior art has recently been reviewed in detail (Rubber Chem. Techn. 69,462 (1996). Multifunctional initiators carrying the above describedtertiary functional groups have also been used to produce multiarm-starbranched polymers (J. Polymer Sci., Chem. October 1997).

[0005] The above discussed living initiating systems producehalide-functionalized polymers, which can be further modified to yieldother functional groups such as hydroxy- or ester. Unfortunately, theseinitiators are usually not available commercially and have to besynthesized by multistep synthetic routes.

SUMMARY OF THE INVENTION

[0006] The inventor has discovered that epoxides, when reacted withLewis acids in the presence of olefins such as isobutylene and styrene,effectively initiate the carbocationic polymerization of those olefins.Epoxides are commercially available or can be synthesized by oxidizingolefins by a simple and fast process (e. g., reacting the olefin withm-Cl-perbenzoic acid in a polar solvent at room temperature, completingthe reaction in a few minutes. P. Dreyfuss and J. P. Kennedy: AnalyticalChem. 47(4), 771 (1975)). Epoxides are known to undergo polymerizationthemselves, by cationic, anionic or coordination mechanism, to yieldpolyethers containing oxygen in the main chain. Epoxi-ethane undergoesliving anionic polymerization yielding a polyether, but substitutedepoxides suffer side reactions. (Encyclopaedia of Polymer Science andEngineering, 2^(nd) Ed., Mark, Bikales, Overberger, Menges Eds., 14,634, John Wiley&Sons, 1985). In the present invention, epoxides,preferably substituted epoxides, initiate the living polymerization ofolefins yielding hydrocarbon polymers, instead of undergoingself-polymerization. Thus the epoxide initiating systems of the presentinvention produce hydrocarbon polymers with hydroxy functionality;multifunctional epoxides will produce multiple hydroxy functionalities.There is no prior art for using epoxides as initiators for the cationicpolymerization of olefins.

[0007] Thus according to one aspect of the invention, there is provideda carbocationic polymerization process for producing a polyolefinpolymer or copolymer carrying oxygen-containing functional group(s)(e.g., hydroxy or aldehyde) group(s), which comprises introducing amonomer charge, a Lewis acid as coinitiator and an organic epoxidecompound as initiator into a suitable reaction vessel and polymerizingthe monomer charge at a temperature of from about 0 degrees to about−120 degrees centigrade to form the terminally functional polymer. Themonomer charge comprises the concurrent and/or sequential addition ofisobutylene and a second monomer selected from the group consisting ofconjugated diolefins and vinylidene aromatic compounds, and the epoxideinitiator is charged in an amount of from 10⁻⁶ to about 10⁻¹ moles permole of the isobutylene.

[0008] According to another aspect of the invention, there is provided aliving carbocationic polymerization process for producing a polyolefinpolymer or copolymer carrying oxygen containing functional groups (e.g.,hydroxy or aldehyde group(s)), which comprises introducing a monomercharge, a Lewis acid as coinitiator and an organic epoxide compound asinitiator, a proton trap to prevent protic initiation, and an electronpair donor which may or may not be necessary to achieve livingconditions, into a suitable reaction vessel and polymerizing the monomercharge at a temperature of from about 0 degrees to about −120 degreescentigrade to form the terminally functional polymer. The monomer chargecomprises the concurrent and/or sequential addition of isobutylene and asecond monomer selected from the group consisting of conjugateddiolefins and vinylidene aromatic compounds and the epoxide initiator ischarged in an amount of from 10⁻⁶ to about 10⁻¹ moles per mole of theisobutylene.

[0009] Another view of the invention is that it provides a new class ofinitiators for inducing the cationic polymerization of olefins. Theseinitiators, in conjunction with Lewis acids as coinitiators, effectivelyinitiate the carbocationic polymerization of olefins. The new initiatorsare epoxides with the general formula

[0010] where R₁, R₂and R₃ are hydrogen, alkyl, aryl or aralkyl groups,and can be the same or different, and i is a positive whole number. TheLewis acid has the general formula of MtX_(n) where M is titanium,aluminum, boron or tin, X is a halogen, an alkyl or an alcoxy or amixture thereof. The process is a carbocationic process, which can beliving or non-living, at a temperature of from about 0 to −80 C. Thepolymer produced can be a homo- or copolymer (random or block) carryinghydroxy functional groups.

[0011] Further aspects of the invention and additional details andexamples will be provided or will become apparent in the detaileddescription which follows.

DETAILED DESCRIPTION

[0012] Tertiary carbocations that are formed by the interaction of aninitiator carrying a tertiary functional group, and a Lewis acid such asBCl₃ or TiCl₄, were shown to be effective initiators for thecarbocationic polymerization of olefins. Such an initiator is2,4,4-trimethylpentyl chloride in conjunction with TiCl₄. In her searchfor commercially available initiators the inventor has theorized thatsubstituted epoxides may be effective initiators for livingcarbocationic polymerizations. It is taught that epoxides may undergocleavage under acidic or basic conditions, and the cleavage is orientedin substituted epoxides: (Morrison&Boyd: Organic Chemistry, 6^(th) Ed.,483 Prentice Hall, 1992)

[0013] Epoxides are also known to polymerize to form polyethers. Thispolymerization reaction forms the base of commodity bonding compoundssuch as epoxy resins. The challenge was to find conditions under whichtertiary carbocations forming from a substituted epoxide in conjunctionwith a Lewis acid would initiate the carbocationic polymerization ofolefins instead of undergoing self-polymerization.

[0014] The inventor has found that compounds such as2,4,4-trimethylpentyl-1,2-epoxide, as 2,4,4-trimethylpentyl-2,3-epoxide,alpha-methylstyrene epoxide and squalene epoxide in conjunction with aLewis acid such as TiCl₄ are effective initiators for the polymerizationof olefins such as isobutylene.

[0015] Without wishing to be bound by the theory, initiation is proposedto take place by the following sequence of reactions:

[0016] The carbocation initiates the polymerization of the olefin, ormay undergo competitive self-polymerization. This latter side reactionmay decrease the initiator efficiency, but the side product was foundnot to influence the living nature of the polymerization. Since openingthe epoxi ring requires at least one TiCl₄ per epoxide ring, effectiveinitiation was found to require the use of excess Lewis acid. Upontermination of the polymerization by methanol, the following reaction isproposed to take place:

[0017] The polymer formed will then contain one hydroxy head group andone chlorine end group. By the use of di- or multifunctional initiators,polymers carrying multiple hydroxi groups can be prepared in one step.

[0018] The carbocationic polymerization of olefins is carried out at lowtemperature (−30 to −100 C.) in a single solvent or solvent mixture ofsuitable polarity. Single solvent can be n-butylchloride, while mixedsolvents contain a nonpolar component such as hexane and a polarcomponent such as methylchloride. It is also taught by the prior artthat internal or external electron pair donors have beneficial effectson the polymerization such as narrowing the molecular weightdistribution or preventing side reactions. Without wishing to be boundby the theory it is proposed that the epoxide-based initiating systemsbehave like internal electron pair donors due to the presence of theoxygen. However, the addition of external electron pair donors such asDMA may be beneficial, but will slow down the polymerization.

[0019] The epoxide initiators of the present invention can easily besynthesized from commercially available olefins, polyolefins orterpenes. For instance, 2,4,4-trimethylpentyl-1,2-epoxide wassynthesized by reacting m-chloroperbenzoic acid with2,4,4-trimethylpentene for 10 minutes at room temperature in methylenechloride solvent. Similarly, epoxidized alpha-methylstyrene andhexaepoxy squalene was synthesized by reacting alpha-methylstyrene andsqualene with m-chloroperbenzoic acid for 10 minutes at room temperaturein methylene chloride solvent. The products were characterized by NMRspectroscopy and were found to be fully epoxidized. The epoxides werefound to be stable for a few months when stored in a refrigerator; after4 months only one epoxide ring cleaved in the hexaepoxi squalene.

[0020] These initiators then were used to initiate the carbocationicpolymerization of isobutylene.

[0021] The following examples describe the present invention. Allpolymerizations were carried out in a dry box under dry nitrogen, in athree-neck flask equipped with an overhead stirrer, immersed in acooling bath at −80 C.

EXAMPLE 1

[0022] The reaction vessel was charged with 50 ml hexane and cooled to−80 C. 54.9 ml condensed methyl chloride was added, followed by theaddition of 0.07 ml (4×10⁻⁴ mol) alpha-methylstyrene epoxide as aninitiator, 0.16 ml 2,6-di-tert-butylpyridine (DtBP) as a proton trap toprevent protic initiation, and 16 ml isobutylene (IB) as a monomer. Thepolymerization was started with the addition of 0.36 ml TiCl₄. Themonomer conversion was 70% in 120 minutes, yielding a polyisobutylene(PIB) with M_(n)=43,000 and M_(n)/M_(w)=1.2. The incorporation of thearomatic initiator was verified by SEC coupled with UV spectroscopy. Thepolymerization was living; the M_(n) increased linearly with conversion,and M_(n)/M_(w) decreased as expected. Table 1 lists the data. TABLE 1IB polymerization initiated with epoxidized alpha-methylstyrene TimeM_(n) M_(n)/M_(w) 5 3900 1.7 10 6100 1.7 15 8000 1.6 20 10,500 1.5 3015,000 1.4 60 27,000 1.3 120 43000 1.2

EXAMPLE 2

[0023] The reaction vessel was charged with 50 ml hexane and cooled to−80 C. 33.4 ml condensed methyl chloride was added, followed by theaddition of 0.73 ml (5.4×10⁻⁴ mol) 2,4,4-trimethylpentyl-1-epoxide as aninitiator, 0.2 ml 2,6-di-tert-butylpyridine (DtBP) as a proton trap toprevent protic initiation, and 13,8 ml isobutylene (IB) as a monomer.The polymerization was started with the addition of 0.13 ml TiCl₄. Themonomer conversion was complete in 40 minutes, yielding apolyisobutylene (PIB) with M_(n)=64,000 and M_(n)/M_(w)=1.1.

EXAMPLE 3

[0024] The reaction vessel was charged with 50 ml hexane and cooled to−80 C. 33.4 ml condensed methyl chloride was added, followed by theaddition of 0.07 ml (4×10⁻⁴ mol) alpha-methylstyrene epoxide as aninitiator, 0.2 ml 2,6-di-tert-butylpyridine (DtBP) as a proton trap toprevent protic initiation, and 16 ml isobutylene (IB) as a monomer. Thepolymerization was started with the addition of 0.5 ml TiCl₄. Themonomer conversion was 80 in 30 minutes, yielding a polyisobutylene(PIB) with M_(n)=66,000 and M_(n)/M_(w)=1.3. The polymerization wasliving; M_(n) increased linearly with conversion and M_(n)/M_(w)decreased as expected. Table 2 summarizes the data: TABLE 2 IBpolymerization initiated with epoxidized alpha-methylstyrene Time M_(n)M_(n)/M_(w) 2 15,000 1.6 4 25,000 1.4 6 35,000 1.3 8 43,000 1.3 1049,000 1.3 20 64,000 1.3 30 66,000 1.3

EXAMPLE 4

[0025] The reaction vessel was charged with 50 ml hexane and cooled to−80 C. 34 ml condensed methyl chloride was added, followed by theaddition of 0.7 ml (4×10⁻³ mol) alpha-methylstyrene expoxide as aninitiator, 0.16 ml 2,6-di-tert-butylpyridine (DtBP) as a proton trap toprevent protic initiation, and 16 ml isobutylene (IB) as a monomer. Thepolymerization was started with the addition of 0.72 ml TiCl₄. Themonomer conversion was 70% in 30 minutes, yielding a polyisobutylene(PIB) with M_(n)=11,000 and M_(n)/M_(w)=1.2. The incorporation of thearomatic initiator was verified by SEC coupled with UV spectroscopy.This polymer was also subjected to GC-MS analysis, which yieldedoxygen-containing aromatic residues. This indicates that the headgroupof the polymer contains oxygen as shown in reaction (2).

EXAMPLE 5

[0026] The reaction vessel was charged with 153 ml methylcyclohexane andcooled to −80 C. 60 ml condensed methyl chloride was added, followed bythe addition of 5×10⁻⁴ mol hexaepoxy squalene as an initiator, 0.32 ml2,6-di-tert-butylpyridine (DtBP) as a proton trap to prevent proticinitiation, and 60 ml isobutylene (IB) as a monomer. The polymerizationwas started with the addition of 3×10⁻² mol TiCl₄. The monomerconversion was 100% in 20 minutes, yielding a polyisobutylene (PIB) withM_(n)=115,000 and M_(n)/M_(w)=1.2 by SEC-Multiangle Light Scattering(MLS) analysis. The slope of the radius of gyration vs molecular weightplot was found to be 0.33, indicating that the polymer has astar-branched structure (spherical shape). Assuming six arms, each armwould have M_(n)=20,000.

EXAMPLE 6

[0027] The reaction vessel was charged with 153 ml methylcyclohexane andcooled to −80 C. 60 ml condensed methyl chloride was added, followed bythe addition of 4.5×10⁻⁵ mol hexaepoxy squalene as an initiator, 0.32 ml2,6-di-tert-butylpyridine (DtBP) as a proton trap to prevent proticinitiation, and 43 ml isobutylene (IB) as a monomer. The polymerizationwas started with the addition of 2×10⁻² mol TiCl₄. The monomerconversion was 55% in 480 minutes, yielding a polyisobutylene (PIB) withM_(n)=174,000 and M_(n)/M_(w)=1.2 by SEC-MLS. The radius of gyration vsmolecular weight plot yielded a slope of 0.32, indicating a sphericalshape star-branched polymer. Assuming 6 arms, each arm would have anM_(n)=30,000.

EXAMPLE 7

[0028] The reaction vessel was charged with 153 ml methylcyclohexane andcooled to −80 C. 60 ml condensed methyl chloride was added, followed bythe addition of 5×10⁻⁴ mol hexaepoxy squalene as an initiator, 0.32 ml2,6-di-tert-butylpyridine (DtBP) as a proton trap to prevent proticinitiation, and 43 ml isobutylene (IB) as a monomer. The polymerizationwas started with the addition of 3×10⁻² mol TiCl₄. The reaction wasallowed to proceed for 250 minutes, at which point 0.32 ml DtBP and0.001 mol dimethyl acetamide DMA as an Electron Pair Donor ED were addedto the mixture, followed by the addition of the prechilled mixture of9.6 g distilled styrene and 10 g methylcyclohexane. The reaction wasallowed to proceed for 20 minutes, at which point methanol was added toterminate the polymerization. NMR analysis of the product showed thepresence of 10.2 mol % (17.4 wt %) styrene in the block. The isobutyleneconversion was found to be 78% in 35 minutes. The polyisobutylene (PIB)had M_(n)=106,700 and M_(n)/M_(w)=1.4, measured just before the styreneincorporation by standard SEC with universal calibration. The finalproduct had M_(n)=125,000 and M_(n)/M_(w)=1.2, measured by SEC-MLS. Theradius of gyration vs molecular weight plot yielded a slope of 0.4,indicating a star-branched block copolymer with spherical shape.Assuming six arms, each arm should have a polyisobutylene section withM_(n)=18,000 and a polystyrene section with M_(n)=2900.

What is claimed:
 1. A star-branched polyolefin homo-, random or blockcopolymer comprised of monomer(s) polymerizable by carbocationicmechanism, having oxygen-containing functional group(s) attached to amultifunctional initiator moiety derived from epoxidized olefins at thecore of the polymer.
 2. A copolymer as recited in claim 1 , wherein saidmultifunctional initiator is derived from epoxidized synthetic ornatural polyisoprenes (terpenes).
 3. A copolymer as recited in claim 1 ,where said epoxidized terpene is hexaepoxy squalene.
 4. A copolymer asrecited in claim 1 , with an M_(n) from about 500 to about 5×107, and amolecular weight distribution (MWD) from about 1.01 to about
 20. 5. Acopolymer as recited in claim 2 , with an M_(n) from about 500 to about5×107, and a molecular weight distribution (MWD) from about 1.01 toabout
 20. 6. A copolymer as recited in claim 3 , with an M_(n) fromabout 500 to about 5×107, and a molecular weight distribution (MWD) fromabout 1.01 to about 20.